-
A cost-effective and scalable system of sensors installed on buses in Valladolid detects, in real time, pollution hotspots that remain invisible to fixed monitoring stations.
-
The data generated help design more effective traffic policies and reduce the population’s actual exposure to pollution.
Bus station in Valladolid / Lourdes Cardenal
A study by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC) and the Institute for Cross-Disciplinary Physics and Complex Systems (IFISC, UIB-CSIC) shows that installing mobile fine particle (PM2.5) sensors on urban buses makes it possible to obtain detailed real-time maps of air quality. The results, obtained after deploying sensors on three buses in Valladolid over seven months, overcome the limitations of fixed monitoring stations, whose data are spatially restricted, and reveal pollution patterns during rush hours, in winter and at high-traffic intersections.
“This is a cost-effective and scalable system that would allow any city to identify, street by street, the most dangerous hotspots for respiratory health and design more effective traffic policies,” the researchers explain.
PM2.5 refers to microscopic airborne particles with a diameter of 2.5 micrometres or smaller, making them invisible to the naked eye but especially harmful to human health. They mainly originate from traffic, industrial activities and combustion processes and, due to their small size, can penetrate deep into the lungs and even enter the bloodstream. These particles are associated with respiratory and cardiovascular diseases, as well as an increased risk of premature mortality, making them a key indicator of air quality in urban environments.
For the study, carried out within the framework of the CSIC PTI Mobility platform, the research team deployed sensors on three urban buses in Valladolid over a seven-month period. These mobile devices continuously measured fine particles while travelling through different neighbourhoods, generating more than one million data points. After calibration and validation against reference monitoring stations, the sensors showed a high level of agreement with official measurements, confirming their reliability despite their lower cost.
“Mobile monitoring allows us to go beyond the limitations of fixed stations and capture how pollution really varies across the city in real time,” explains José Ramasco, researcher at IFISC (UIB-CSIC) and one of the lead authors of the study published in the scientific journal IEEE Internet of Things Journal. “This approach reveals patterns that would otherwise remain hidden.”
Teresa Moreno, researcher at IDAEA-CSIC and coordinator of the study, highlights the value of this approach for assessing urban exposure: “These systems bring us much closer to the reality of population exposure by providing street-scale information under real mobility conditions, allowing us to develop more specific and effective mitigation strategies.”
Beyond fixed monitoring stations
Unlike traditional air quality monitoring stations, which provide highly accurate but spatially limited data, sensors installed on buses make it possible to generate dense maps of pollution levels along streets and transport routes. The results revealed clear daily and seasonal trends. PM2.5 concentrations peaked during morning and evening hours, likely linked to traffic activity, and were consistently higher in winter due to atmospheric conditions that favour the accumulation of pollutants close to the ground.
The study also identifies localised pollution hotspots, particularly near busy intersections, high-traffic corridors and bus stops where vehicles frequently accelerate and brake. These small-scale variations are difficult to detect using fixed monitoring networks alone, yet they are essential for understanding the population’s real exposure.
“Cities can use this information to design smarter traffic policies or guide citizens towards less polluted commuting routes,” the authors point out.
The research team highlights that integrating data from mobile sensors with existing monitoring networks can significantly improve decision-making. Although low-cost sensors require careful calibration and maintenance, their ability to provide continuous, high-resolution coverage makes them a valuable complement to traditional systems.
The study, funded by the Next4mob project of the State Research Agency–Ministry of Science, Innovation and Universities, also points to some practical challenges: sensor maintenance, occasional device failures or interruptions in data collection due to bus inactivity. Nevertheless, according to the researchers, these limitations can be mitigated through the use of redundant sensors and robust system design.
González-de-Castro, I., Viana, M., Ramasco, J. J., Maín-Nadal, A., and Moreno, T. (2026). Air Quality Mapping Using PM2.5 Sensors on Urban Buses. IEEE Internet of Things Journal. DOI: doi.org/10.1109/JIOT.2026.3672932
More news
